1. Field of the Invention
This invention relates to a metal cleaning process for removing metal deposits and more particularly, an electrochemical process and apparatus for removing refractory metal deposits on deposition equipment parts used in semiconductor fabrication.
2. Prior Art
Chemical vapor deposition (CVD) is defined as the formation of non-volatile solid film on a substrate by reaction of vapor phase chemicals (reactants) that contain the required constituents. The reactant gases are introduced into a reaction chamber and are decomposed and reacted at a heated surface to form a thin film. A wide variety of thin films utilized in very large scale integration (VLSI) fabrication are prepared by CVD.
Typically, refractory metal films are deposited on substrates using any number of well-known vapor deposition processes. The deposition technology and equipment used to prepare such films by CVD are well-known in the semiconductor industry. Furthermore, the thin films created by CVD are used in a variety of different applications in VLSI fabrication and may be prepared using a variety of techniques. However, the method by which they are formed must meet certain requirements. The process must be economical, that is, it must be capable of producing a high through-put. Additionally, the resulting films must exhibit some of the following characteristics: (a) good thickness uniformity, (b) high purity and density, (c) controlled composition and stoichiometries, (d) high degree of structural perfection, (e) good electrical properties, (f) excellent adhesion and (g) good step coverage.
All of these characteristics depend in part on the capabilities of the equipment used. Additionally, contaminants in the system reaction chamber could generate particles, which are then deposited onto the wafers and produce lower yields. The lower yields result in poor electrical properties, including electrical breakdown. Furthermore, purity of the film suffers as well as the film uniformity.
After a number of through-puts some of the deposition equipment used within the reaction chamber itself, such as the chucks and clamps, become coated with refractory metal deposits. The metal parts, typically fabricated from Monel.RTM. become coated with a thin layer of tungsten. Monel.RTM. is the trademark used by International Nickel Co., Inc. for a metal alloy containing nickel and copper. The refractory metal deposits on the deposition parts encumber the efficiency of the equipment, as well as produce particles that then flake off and are deposited on the wafers.
Typically, there are several means of avoiding the problem of refractory metal deposits. One way, and generally the most expensive way, is to completely replace the deposition parts with new manufacturer's parts.
Another way of dealing with the coated parts, is to return them to the manufacturer to be remachined. While this is useful in that the manufacturer will remachine the parts, thus removing the metal coating, the parts are eventually destroyed and may only be used once again. Furthermore, the cost is almost as prohibitive as purchasing new parts.
A third way, traditionally used is to bead blast the parts. This is done by using a micro bead blaster. Generally, selection, size and composition of the bead must be considered when determining the suitability of bead blasting. These factors determine the extent of efficiency of the blasting technique for removing the deposited metal. They are also indicative of the expected extent of damage inflicted on the parts as a result of bead blasting. Additionally, the economic disadvantage of manufacturer's remachining or purchasing of new parts is essentially the same, in that it is costly and eventually destructive.
Typically, bead blasting of the coated parts is performed only once since this technique leads to their destruction. Among other things, bead blasting damages the parts by pitting the surface. This degrades sealing capabilities of the parts and drastically shortens the life expectancy of the parts. This eventually leads to a degradation of the performance of the assembled process equipment, which in turn, results in a reduced yield of semiconductors devices.
Disadvantageously, the current bead blasting techniques require approximately 24 hours of down time per part set. On the average, the cleaning and discarding of the parts after one cleaning process currently used, requires 8 to 12 sets of deposition parts per year per deposition chamber.
Therefore, what is needed is a method of cleaning the deposition equipment parts without causing structural damage to these parts as well as decreasing the part cleaning through-put time. The present invention provides an electrochemical approach to replace the mechanical bead blasting of cleaning the parts currently used. The refractory metal is dissolved from the surface of the parts using an electrochemical process.